This invention relates to engine air intake shutoff valves. More particularly, this invention concerns a gate valve having a loose-fitting gate member that can seat against one seating surface to restrict air flow into a combustion engine or an opposed seating surface to contain an intake manifold explosion.
It is well known to provide an engine air intake shut-off valve between the air induction system and the intake manifold of an internal combustion engine. The primary function of an engine air intake shut-off valve is to protect against two serious engine malfunctions, overspeed and intake manifold explosion.
Engine overspeed may occur when there is a sudden load drop on the engine that permits an abrupt acceleration of the engine. If this occurs, the governor can usually react to regain control of the engine. In its more serious form, overspeed occurs when the engine receives fuel from another source. This most commonly occurs by induction of combustible vapors from the atmosphere. Another source of fuel is the turbo-charger oil seals, or the engine may suck fuel from an oil bath air cleaner. In the worst overspeed situation, the engine may accelerate to total destruction.
Shutting off the main fuel supply has little effect on a serious overspeed condition. The only safe solution is to shut off the air supply to the engine.
The second engine malfunction, intake manifold explosion, is created when combustible vapors have been induced into the intake manifold and are drawn into the cylinder and ignited on the intake stroke by hot spots in the cylinder prior to intake valve closing. An explosion can also occur during engine shutdown if an air intake shut-off valve momentarily pops open, allowing a fresh surge of combustible vapors to be introduced into the combustion chamber where there is a hot, fuel-rich mixture that may explode.
Various air intake shut-off valve designs are currently in use, including butterfly valves, in-line spring loaded valves, and sliding gate valves. Shut-off valves of the sliding gate type are preferred for two reasons. First, unlike butterfly and in-line spring loaded valves, sliding gate valves do not tend to pop open during shutdown, thus reducing the chances of an intake manifold explosion. Second, butterfly valves frequently fail under the pressures created by an intake manifold explosion. Sliding gate valves, by contrast, provide a much more substantial closure of the air intake line which can withstand these high pressures.
The main disadvantage of present sliding gate valves is that they are designed with a gate member that fits snugly between two opposed sealing surfaces in the valve body. Because of this tight fit, dirt can accumulate in the valve which inhibits free movement of the valve to the closed position. Thus, these valve designs require frequent maintenance to maintain valve operability.
Further, present gate valve designs require a positive sealing element such as an O-ring to provide a tight seal between the gate member and the valve housing. These sealing elements can wear and fail over time and must eventually be replaced.